nuclear recoil

Nuclear recoil occurs when a nucleus is bombarded by a particle, causing a change in its identity or characteristics. This bombarding particle, such as an alpha particle, neutron, or proton, must possess enough energy to overcome the nucleus's positive charge and interact with the strong nuclear force.1

In this process, a target nucleus and a bombarding particle produce a new, heavier nucleus and an ejected particle. For instance, Ernest Rutherford observed that bombarding nitrogen with alpha particles resulted in protons and oxygen isotopes.1

Recoil is also relevant in electromagnetic radiation. When an atom emits or absorbs a photon, it recoils, similar to a cannon recoiling after firing a shot. This recoil carries away kinetic energy, affecting the energy of the emitted or absorbed photon. For gamma-ray photons, this recoil energy is significant, preventing resonance absorption by free nuclei. However, recoilless absorption is possible when nuclei are embedded in a solid, allowing the entire solid to absorb the recoil momentum.2